Amplifier



April 1930. P. c. GARDINER 1,752,839

AMPLIFIER Filed Feb. 26, 1929 Fig. 2.

Inventor: Paul C. Gardiner,

His Attorney.

Patented Apr. 1 1,' 1930 UNITED STATES PATENT orrlcn PAUL C. GABDINEB, OI OAKLAND, CALIFORNIA, ABSIGNOB TO GENERAL We GORP-ANY, .A CORPORATION NEW YORK mnrmn Application filed rebmri :0, 1929. Serial No. 342304.

The resent invention relates to an amplifier em odying electric discharge devices, and has for its object to provide an improved and simplified amplifier which'is adapted to receive its operating potentials directly from a source of unrectified alternating current for voltages or signals, where the use of batteries to supply operating potentials involves considerable attention or frequent replacement, and where the cost of a rectifying means for an alternating current supply is not justified.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a wiring diagram of an amplifier .embodying the invention and adapted for direct current control; and Fig. 2 is a wiring diagram of the same amplifier adapted for alternating current control.

Referring to Fig. 1, 5 and 6 are electric dis charge devices providing the initial and output stages of the amplifier and representing any suitable number of stages in an amplifier. These devices are shown by way of example as being of the usual 3-element hot cathode type although other types of such devices may be used. Tube 5 is preferably of the highmu type having a control grid 7, a cathode 8 heated from a suitable source of current such as alternating current supply leads 9, and an anode 10, while 6 is a suitable output tube having similar elements 11, 12 and 13 for which "similar cathode heating supply leads 14 are provided. These tubes may be of any suitable type however, and may be operated from any suitable source of heating current.

The amplifier operates a relay or other suitable current responsive device 15 connected in the output or anode circuit 160i tube 6. Direct current control voltage to be amplified for operating the relay is applied between the grid and filament of the initial or input tube 5 through control leads 17 and 18,

representing any suitable control circuit,

supplying alternating lead 17 being connected with the rid of tube 5 and lead 18 being connecte cathodes of both tubes through suitable leads 19 whichin the resent example are tapped into the electrica center of the cathode supply leads as indicated.

aw or unrectified alternating current for operatin voltages to the amphfier is supphed throug current terminals 20'between which is connected a resistance network including a potentiometer or resistor 21 having a contact 22 which is movable between the terminals of the potentiometerl Contact 22 is connected through a cathode return lead 23 with leads 18 and 19 and the cathodes. Leads 18 and 23 together with leads 19 form a common anode and grid -return lead or circuit for the amplifier.

The anode circuits of both tubes are connected with one terminal of the alternating current'supply and one terminal of the potentiometer 21 through a lead 24, the anode circuit of. tube 6 including the relay 15, and the anode circuit of tube 5 including an anode resistor 25. The other oropposite terminal of the alternating current sup ly and the remaining terminal of the potentiometer are connected through a grid resistor 26, with the grid of tube 6.

The high potential ends of the resistors 25 and 26, that is, the anode andgrid endsof said resistors, are connected through a resistor 27 which also conductively connects anode 10 with grid 11. The closed loop re-.

sistance network thu completed, serves to connect the amplifier t bes in cascade and to supply operating voltages thereto, the arrangement being such that voltages amplified by tube 5 and established. across anode alternating with the resistor 25, are applied across grid bias resistor 26 and directly to grid 11 of the sue- .ceeding tube through the conductive coupling means provided by resistor 27.

If the resistor 27 were not provided and the grid 11 were connected directly to the plate of the preceding tube 5 the potential of the grid 11 would be as positive as the plate of tube 5 during part of each cycle. The resistor 27 thus keeps the grid of tube 6 mostly resente age applied in the negative range of grid potentials, since,

'are positive and negative, as indicated in the drawing by the positive and negative signs in solid, it will be seen thatthe anodes will have a ositive voltage applied to them, rep- 5 by the voltage across the potentiometer between the contact 22 and the positive terminal, while the grid of output tube 6 will have a negative potential represented by the voltage between contact 22, and the negative terminal applied to it, During each neglative half cycle indicated by the positive an negative signs in dotted, no anode current will flow. The grid voltage applied between the sliding contact 22 and the connection of grid 11 with the potentiometer 21 may be varied by movin contact 22 along the potentiometer. The direct current control voltto the input circuit represented by control leads 17 and 18 is amplified and will cause a variation in the anode current of the output tube to operate relay 15.

Viewed in another aspect, the resistance network including potentiometer 21 and resistors 25, 27 and 26 in the order named, provide a bridge circuit one arm of which is connected with the supply terminals and the opposite arm of which is connected at its ends with the anode and grid of two different amplifier devices. The amplifier having its grid so connected is the output device and this has its anode circuit connected between one end of the first named arm and a point intermediate its ends. The intermediate connection servesas a cathode connection for the am lifier devices.

e sensitivity of the amplifier may be made relatively high by the use of a highmu tube at 5. For example, it has been found that when operating an amplifier substantially as described with a highmu tube at 5, and a suitable output tube at 6, in connection with a relay where the applied alternating voltage across terminals 20 was in the ne1 hborhood of 220 volts, with 7 megohm gri and anode circuit resistors 25 and 26, and with coupling resistor 27 of a value approximately 2 megohms, an amplification of approximately 15 could be obtained from grid to grid. This was with a setting on the potentiometer such that the anode voltage was substantially while the negative grid voltage was substantially 30. The

low anode voltage is due to the resistance at 25 and 26. However, different values of resistance may be used. With this arrangement a very small change in D. C. potential applied to id 7 of tube 5 through the control circuit 1 -18 produced a response in the out- PUit anode circuit sufiicient to operate the re a It should be understood that the resistance, voltage and amplification values above given are only by way of example as representing one group of a plurality of suitable resistance and voltage values which depend upon the ty e of tubes employed, and the operating vo tage which is available, as well as the amount of amplification which is required between the control circuit and the output or anode circuit in which the current res onsive device is located.

eferring now to Fig. 2, the amplifier of Fig. 1 bearing the same reference numerals throughout, is shown in connection with an alternating current control circuit. The amlifier tubes 5 and 6 are connected in cascade y resistors 25, 26 and 27 and supplied with alternating operating potentials from terminals 20 through the otentiometer 21 for the operation of the re ay 15 in the output or anode circuit of tube 6. The conductor 231819 is the common cathode return circuit for the amplifier. An alternating current control circuit for the amplifier is represented by leads 28 and a resistor,29 connected between them, across which resistor an alternating voltage is developed'b the current flowing through it from lea s 28. The input circuit is connected at one terminal with the grid 7 of the input tube through a stopping condenser 30 while the remaining terminal is connected with the cathode circuit 18. The grid is connected with the cathode circuit 18 through a grid leak resistor 31.

With this arrangement the alternating voltage is applied through leads 28 to the resistor 29 and by means of the detector grid leak resistor 31 and condenser 30 to the input circuit of the tube 5. In all other respects the operation of this amplifier is the same as described in connection with the D. C. control amplifier of Fig. 1.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An alternating current amplifier including electric discharge devices, alternating current supply terminals, a resistance network including a potentiometer connected between said terminals, anode and grid resistors, connected between said devices and said potentiometer and a coupling resistor connected between said resistors, a cathode return circuit, and a contact movable between the terminals of the potentiometer and connected with the cathode return circuit.

2. An alternating current amplifier ineluding electric discharge devices, alternating current supply terminals, and a closed loop resistance network including a potentiometer and coupling, anode, and grid resistors connecting said devices in cascade and providing a voltage supply means therefor.

3. An alternating current amplifier including electric discharge devices provided with grid and anode circuits, alternating current supply terminals, a resistance network interposed between said terminals and said devices and arranged to form a bridge circuit having four arms connected respectively between said terminals, between the anode of one of said devices and the grid of another of said devices in the anode circuit of one of said devices, and in the grid circuit of another of said devices.

4. In an alternating current amplifier provided with electric discharge amplifier devices. the combination of alternating current supply terminals, a otentiometer connected across said termina s, an anode circuit includin an anode resistor connected with one of sai supply terminals, a grid circuit including a grid resistor connected with the other of said terminals, a cathode return circuit, and a contact movable between the terminals of the potentiometer connected with the cathode return circuit.

5. An alternating current amplifier including electric discharge devices, the combination of alternating current supply terminals, a potentiometer connected across said terminals, a coupling resistor connected between the controlled and controlling elements of two-of saiddevices, an anode circuit including an anode, resistor, said resistor being connected at one end WIth OIIG term nal of said potentiometer and connectedat its opposite 'end with; said] coupling resistor, a

grid circuit including a grid resistor, said resistor being connected at one .end with the other of said terminals of the potentiometer, and connected at its opposite end with said coupling resistor, a cathode return circuit, and a contact movable between the terminals of the potentiometer connected with cathode return circuit.

6. An alternating current amplifier including electric discharge devices provided with grid and anode circuits alternating current supply terminals, a coupling resistor connected between the "anode circuit ofone 'of said devices and the grid circuit of the other of said devices, an anode resistor consponsive device in said circuit, a potentiom-' eter connected across said alternating current supply terminals, a cathode return lead, and 66 a. contact movable between the terminals of nected between one of said terminals and one said potentiometer connected with said cathode return lead.

7. An alternating current amplifier including electric discharge amplifier devices,

alternating current supply terminals, a coupling resistor, an anode resistor connected between one of said terminals and one terminal of said couplin resistor, a grid resistor connected between t 'e other of said terminals and the remaining terminal of said coupling resistor, an output anode circuit connected with the first named alternating current supply terminal, a current responsive device in said circuit, a potentiometer connected across said alternating current supply terminals, a cathode return lead, and a contact movable between the terminals of said potentiometer connected with said cathode return lead, an alternating current control circuit including a pair of control leads connected with one of said electric discharge devices and means interposed in said connection for operating said device as a detector.

8. The combination with a pair of electric discharge devices each of which has an anode, a cathode and a control electrode, of a conductive resistance coupling means connecting said devices in cascade, said means being provided with an anode voltage terminal and a grid voltage terminal, means for supplying an alternating voltage between said terminals, an output anode circuit for one of said devices connected with said anode voltage terminal, a current responsive device in said circuit, a otentiometer connected between said terminals, circuitvmeans connecting the cathodes of said devices with sa d potentiometer at a point intermediate sa1d terminals, means for applying an alternating voltage to the grid of another of said devlces, 106

said means being connected between the rid and the cathode of said device and inclu 'ng -a "stopping condenser whereby said device operates as a detector and a grid leak resistor interposed between said grid and said 10 cathode.

AUL C. G RDINER. u 

